Heart rate monitors come with a watch and a chest strap. there are some models that are just the watch and you put your thumb on it and it measures your pulse that way. the chest strap ones are better for continuous measurement, but some people find the chest straps uncomfortable.
the basic HR monitors will ONLY show HR in the display and not time. then there are some that have all sorts of features including down loading info to PC's. the more features the HRM has, the more $$. (and the more bulky the watch part)
the strap goes under the boobs along the heart line.
i don't know about swimming with them, someone else will have to answer that one...
hope that helps!
hannah